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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
| 5 | 7 |
| 6 | 21 |
| 7 | 61 |
| 8 | 403 |
| 9 | 3415 |
| 10 | 36395 |
| 11 | 473261 |
| 12 | 8291363 |
| 13 | 204964495 |
| 14 | 6738662861 |
| 15 | 291876652529 |
| 16 | 16526293766701 |
| 17 | 1250870357604441 |
| 18 | 127503882340930419 |
| 19 | 17331789387120484429 |
| 20 | 3122597067315836972733 |
| 21 | 746394914944854757141353 |
[1,1,1,1,7,21,61,403,3415,36395,473261,8291363, 204964495,6738662861,291876652529,16526293766701, 1250870357604441,127503882340930419, 17331789387120484429,3122597067315836972733, 746394914944854757141353] |